Electromagnetic induction apparatus



1 s. D. MORETON ET AL 3 ELECTROMAGNET I C INDUC T ION APPARATUS FiledMarch" 28, 1946 Inventor s: 1 Stuart D. Mor'etoh, Quinton Shaffer",

Their Attorney.

Patented Nov. 18, 1947 ELECTROMAGNETIC INDUCTION APPARATUS Stuart D.Moreton, Allison Park, and Quinton Shaffer, Philadelphia, Pa., assignorsto General Electric Company, a corporation of New York Application March28, 1946, Serial No. 657,696

3 Claims.

Our invention relates to electro-magnetic induction apparatus andparticularly to a structure for mountingsuch apparatus.

Our invention is especially adapted for use in the mounting of a bushingcurrent transformer which usually consists of a heavy magnet core aroundwhich is wound an insulated winding in which is induced a current thatis proportional to that passing through the conductor of the electricalbushing about which the bushing current transformer is mounted.

Heretofore it has been common practice to mount such a bushing currenttransformer directly to the supporting wall of the bushing by clampingmeans that merely hold it compressively in place. It has been found thatsuch clamping methods result in stressing, -disturbing, and possiblydamaging the insulated Winding on the core.

It is therefore one object of our invention to provide an improvedmounting structure for electromagnetic induction apparatus whereby itmay be mounted without hazard of impairment to the winding or itsinsulation.

It is also an object of our invention to provide an improved mountingstructure for electromagnetic induction apparatus that is simple, safe,reliable, and of low cost.

Another object of our invention is to provide mounting structure havingmembers that extend through the electromagnetic induction apparatus,thereby providing additional or auxiliary support for the apparatus.

Another object of our invention is to provide extended mountingstructure through electromagnetic induction apparatus that serves tosupport additional induction apparatus or devices associated therewith.

A further object of our invention is to provide extended mountingstructure through electromagnetic induction apparatus that serves tosupport cover means, or other ancillary gear incidental thereto.

The advantages of our invention will become apparent from the followingdescription and the accompanying drawing and the features of noveltywhich characterize our invention will be pointed out with particularityin the claim annexed to and forming a part of this specification.

In the drawing, Fig. 1 is a perspective view showing a pair of bushingcurrent transformers mounted and protectively covered by a sheet steelhousing in accordance with our invention; Fig. 2 is an end or axial viewof one of such bushing current transformers, showing a preferredarrangement of the mounting sup-ports relative to the toroidally shapedtransformer body, and Fig. 3 is a cross-sectional view along the lines33 of Fig. 2, showing one method of attachment of the supports to thetransformer core.

In the embodiment depicted in the drawing, instrument currenttransformers made in accordance with our invention are shown as applyingto metal enclosed switchgear, in which the component devices of theapparatus such as the circuit breaker, disconnecting switches, busconductors, etc., are segregated into separate and grounded sheet metalsubcompartments. In this well known type of switchgear it is usual toelectrically interconnect the related devices in adjacent compartmentsby means of conductor bushings which project through the interveningpartitions.

Referring to Fig. 1, a conductor bushing IE projects through a suitableaperture in the partition wall H, and may be assumed to proceed from adisconnecting switch (not shown) that is mounted upon and concealed bythe partition wall I l. The bushing Hi further may be assumed to be acomponent part of thedisconnecting switch so that it is supportedthereby independently from any of the structure shown on the drawing andmay comprise a hollow externally corrugated porcelain cylinder, withinwhich is supported the laminated bars l2 for electricallyinterconnecting the disconnecting switch with another device such as acircuit breaker (not shown) on the near side of the partition I E.

It is conventional practice to mount toroidal type current transformers(familiarly known as B. C. T.s) concentrically about electricalbushings, where the bushing stud or laininations 12 in this embodimentserve as the transformer primary circuit. In accordance with thispractice a pair of B. C. T.s I3 are shown mounted concentrically aboutand independently of the bushing l0. Independent mounting fortransformers and their associated bushings prevent interaction due topossible physical shock stresses that conceivably might be of a damagingnature to either or both.

In this embodiment of our invention, the inde pendent mounting means forthe B. C. T.s i 3 comprise a plurality of formed flat metal supportmembers M which as most clearly shown by Fig. 3 are secured to the heavylaminated toroidal core l5 by means of clamping bands IS. The twoextremities of each support member i i extend beyond the transformerbody and are provided with upturned mounting feet I! and [8 that radiateoutwardly as clearly shown by Fig. 2 so as to form a U-shaped member.Each upturned foot contains a mounting hole. Although four such U-shapedsupporting members are shown, thereby providing mounting holes that areequally spaced around a circle concentric with the B. C. T., it will beunderstood that other variants may best be served by a lesser or greaternumber of mounting members having holes arranged to suit other mountingconditions. We find it preferable to place the two holes in the feet ofeach support member I4 in the same axial alignment as indicated by thecenterline I9 in Fig. 3, and it is also advantageous that a clearancehole be provided in one leg While providing a tapped hole in theopposite leg. Accordingly, Fig. 3 shows the support members I 4 having aplain hole in what may be termed the main mounting foot I8, and aso-called punch-tapped hole in the corresponding auxiliary mounting footI 1.

From the description thus far, and as shown best by Fig. 3, it will beunderstood that a unit B. C. T. made in accordance with our inventioncomprises the toroidal core I5 having a plurality of double-endedmounting members l4 secured thereto by bands I6, together with thesecondary windings and their protective insulation 20 that is coiled andwrapped around the core I5 in a manner well known in the art. Theadvantages of this unitary construction are best appreciated byreference to Fig. 1 from which it will be observed that a single B. C.T. unit can be readily mounted upon the partition wall II by means ofbolts or screws 2| through the main mounting feet I8 and which mountingmay be entirely independent of the bushing about which it is mounted. Itwill be clear that such an arrangement permits the removal or additionof either the B. C. T. or its associated bushing irrespective of thepresence of the other. Obviously this type of mounting is superior tosome prior methods in which the toroidal transformer constructed with nomounting means was merely clamped directly and compressively to thepartition wall, thereby stressing and possibly disturbing or damagingthe comparatively sensitive windings and their insulation.

B. C. Ts are used variously for providing a source of current foroperating instruments, meters, protective relays or breaker trip coilsso that occasionally the provision of more than one transformer perphase is desirable. Fig. 1 illustrates how in such cases transformerswith our novel mounting means are readily mountable one upon the otherbecause as already explained the auxiliary mounting feet I! are made toregister with the main mounting feet l8. Expeditions mounting of thesecond transformer on the first is readily accomplished by entering thescrews 22 through the clearance holes of the main feet I8 of the secondtransformer and screwing them into the tapped holes in the auxiliaryfeet I! of the first transformer without the necessity of providingseparate nuts for the screws 22.

In metal enclosed switchgear it is good practice to protect and isolatethe secondary devices and wiring from the primary apparatus and itsconnections. Accordingly, the B. C. Ts of Fig. 1 are provided with alight boxlike sheet metal enclosure 23. By suitably flanging and weldingits sides and cover, the enclosure 23 may be prefabricated into a unitstructure as shown. Our invention provides a simple, improved, andeconomic means for supporting the protective enclosure 23, because theuse of the projecting auxiliary feet 5! for this purpose obviates anynecessity for providing additional or external fastenings, say on thepartition I I, for the enclosure 23. We therefore simply employ screws24 which engage the tapped auxiliary feet I! of the second transformerfor mounting the protective enclosure 23 in proper relationship aboutthe B. C. Ts I3. For the more usual applications which employ but asingle B. C. T. the outer transformer would be omitted and an enclosuresimilar to but correspondingly shorter than enclosure 23 would beprovided for bolting directly to the auxiliary feet I! of the B. C. T.that is bolted to the partition I I. In such a case a correspondinglyshorter bushing than the bushing l0 shown would be substituted.

In double B. C. T. arrangements, as shown in Fig. l, where thetransformers are comparatively light in weight, or where they aremounted vertically, as for example around a roof entrance bushing, thescrews 24 in the auxiliary feet I! will constitute the sole mountingmeans for the enclosure 23. However, where heavy double B. C. Ts arearranged in cantilever relationship to the partition II as shown in Fig.1, it will be obvious that it may become desirable to afford auxiliarymeans for supporting the overhung weight of the transformers. For thispurpose it becomes convenient to furnish external supporting means forthe enclosure 23 which may be accomplished in a number of differentways. For example, the side sheets of enclosure 23 can be flanged andbolted to the partition I I or, alternatively, the front end of theenclosure 23 can be suspended from the structure above or supported fromthe floor of the compartment below. Assuming therefore the enclosure 23to be externally and satisfactorily supported, the auxiliary feet I!secured by screws 24 to the front cover of enclosure 23 now serve asadditional supporting means for the B. C. Ts I3. It will now be evidentthat-the auxiliary feet I! which are extensions of the supportingmembers I4 may serve either as additional supporting means for thetransformer itself or conversely may serve as the sole or mainsupporting means for the associated enclosure 23.

Referring to Fig. 3, the supporting members I4 are securely andpermanently bound to the tightly wound clock-springlike low-loss siliconsteel core I 5 by means of metallic clamping bands It which encircle thecore I5 and which may be likened to large diameter hose clamps. Asuitable jig is conveniently used for locating the core I5 and theseveral support members I4 in their interrelated positions prior to theapplication tensioning and making fast of the clamping bands I6. Afterthe bands are clamped, a hole is handpunched through the bands I 6 inway of each predrilled hole 25 in the support members I4, after which abrass tubular rivet 26 is driven into and heads up permanently withineach hole 25. The rivets 25 serve as dowels whereby the relativepositions of the supports I4 and bands I6 are ensured. Other means, suchas tack-welding the bands and supports together, would serve the samepurpose. Conceivably, for light B. C. T.s and where mass production iscontemplated, it may be desirable to combine both the supports I4 andtheir clamping bands I6 into an integral structure, as by stamping froma single metal sheet or by welding together prior to clamping about thecore, thereby eliminating any necessity for the above described dowelingoperation. Preferably, the bands I8 are located as shown, that is withtheir outer edges flush or in alignment with the flat end faces of thecore I5 as at 21. As a con- 2 sequence, and in addition to the supportsl4 being held frictionally to the core 15 by the tensioned bands l6,endwise movement of the doweled supports M with respect to the core I5is further restricted due to the abutting relationship of the bands at21 to the end insulation washers 28, which are tightly and insulatinglytaped to the core [5 before the first layer of the secondary winding iscoiled around the toroidal core. The application of successive layers ofinsulation and secondary windings with the usual tap connections andtheir terminals as required (not shown) and as is well understood in theart, complete the entire construction of the B. C. T. unit.

Although we have shown and described a particular embodiment of ourinvention, we do not desire to be limited to the particular embodimentdisclosed and we intend in the appended claims to cover allmodifications which do not depart from the spirit and scope of ourinvention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A supporting structure for a bushing current transformer having atoroidal core and an insulated winding thereon comprising a plurality ofsupporting arms positioned about the outer periphery of said core andprojecting axially therefrom, a plurality of clamping bands secured tosaid supporting arms and disposed about the outer periphery of said coreto hold said supporting arms in position, and means for securing saidarms to a supporting base member.

2. A supporting structure for an electromag- I netic device having atoroidal core and an insulated winding thereon comprising a plurality ofsupporting arms interposed between said core and said winding andextending axially therefrom, a clamping band interposed between saidwinding and said supporting arms and extending around the periphery ofsaid core for securing said supporting arms in position and means forsecuring said arms to a supporting base member.

3. A structure for supporting a plurality of similarly constructedelectromagnetic devices on a common axis, each device having a core andan insulated winding thereon, said structure comprising a plurality ofsupporting arms interposed between the core and winding of each deviceand extending in opposite directions therefrom and disposed insubstantially parallel relationship to the common axis, said arms ofeach device being so disposed with respect thereto as to coincide withand engage the corresponding arms of the adjacent device, means forconnecting the engaging portions of the arms of adjacent devicestogether, clamping means afiixed to said arms for securing said arms inposition between the core and winding of each device, a housing for saiddevices and means for securing the supporting arms extending from eachend device to said housing,

STUART D. MORETON. QUINTON SHAFFER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 667,121 Fleming Jan. 29, 1901755,800 Schmidt Mar. 29, 1904 1,212,755 Fondiller Jan. 16, 19171,569,723 Dickinson Jan. 12, 1926 1,830,541 Harris Nov, 3, 1931

